Bone: Specialized Connective Tissue -very hard ECM -dynamic tissue

1. Bone: Specialized Connective Tissue -very hard ECM -dynamic tissue -resorption and bone development

2. Components of bones: -marrow, hemopoietic organ -periosteum, external surface except articular surface outer dense fibrous connective tissue inner osteoprogentors and osteoblasts -endosteum, central cavity is lined by thin layer of CT with layer of osteoprogentors and osteoblasts -bone itself: cells surrounded by calcified ECM

3. Bone Matrix: inorganic constituents Inorganic component: hydroxyapatite crystals (calcium and phosphate also amorphous) Water Associates with organic component: -type 1 collagen (highly cross-linked and hard to extract) makes bone acidophilic The hydroxyapatite + collagen give hardness and strength If decalcified, becomes soft If organic component is removed, remains hard but brittle.

4. Bone, Amorphous ground substance -stains with PAS, explain glycosaminoglyacans staining with PAS -contains sulfated GAGs Keratin sulfate chondroitin sulfate chondroitin sulfate & kertin sulfate cross links with proteoglycans -> link proteins -> hyaluronic acid. These are called aggrecans composites

5. Glycoproteins of the Bone Matrix Vitamin D is required for the synthesis of these glycoproteins. Osteocalcin binds hydroxyapatite Osteopontin binds hydroxyapatitie and integrins on osteoblasts & osteoclasts Sialoprotein binds matrix components and osteoblast and osteocyte integrins, therefore has and adhering function

6. Cell in bone tissue: Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts

7. Cells of the bone: Osteoprogenitor Cells -located in the inner cell layer of the periosteum, endosteum, Haversian canals -lots during intense bone growth -can become mitotic and differentiate -spindle shaped -pale, oval nucleus -pale cytoplasm

8. Osteoblasts: • -from osteoprogenitor cells • -synthesize bone matrix • -surrounded by uncalcified bone matrix (osteoid) • -located on the bone surface, • -cuboidal to columnar • -communicate by gap junctions • -can be quiescent (bone lining cells) • Immediately surrounded by noncalcified layer, • (osteoid-uncalcified bone matrix) • -

9. The mb of osteoblasts • -have integrins with parathyroid hormone receptors that bind pt • Osteobl secrete OPGL, osteoprotegerin ligand. • OPGL induces osteoclast differentiation • Osteobl secrete osteoclast stimulating factor • stimulates osteoclast to resorb bone • Also osteobl secrete enzs to remove osteoid •  Osteoclast contact bone to remove it

10. Osteocytes: -incarcerated osteoblasts -in lacunae of calcified ECM -have processes, in bone tunnels, canaliculi -gap junctions -not very active, only secrete material for bone maintenance Tension placed on bone  osteocy. Release cAMP, Osteocalcin and insulin like growth factor osteoblasts Are recruited bone formed (remodeling)

11. Osteoclasts: -responsible for bone resorptionapoptosis after -multinucleated -originate from bone marrow granulocyte macrophage progenitors -have receptors for parthyroid hormone, calcitonin, OPGL and other factors -osteoprotegerin from inhibits osteocl diff & fn

12. How do osteoclasts resorb bone? • Osteocl CA forms carbonic acid •  CO2 and H2O • H+ and HCO3- • H+ transported to ECM • acid environment • mineral dissolved • Dissolved minerals to capillaries

13. Bone Structure: Long bones - Compact Bone on the surface - very dense, has Haversian systems Spongy Bone lines the marrow cavity - has traberculae And spicules

14. In compact bone: Haversian Canal systems - Haversian Canal carries blood vessels, nerve fibers - Volkmann Canals join parallel Haversian Canals - canals are lined by progenitors and osteoblasts - lamellar organization of osteocytes